Solvent refining hydrocarbon oil



July 4, 1939. B. Y. MccARTY ET AL SOLVENT REFINING HYDROCARBON OIL Filed Nov. 5, 1956 NTOR III

BERNARD Y MECARTY HOWARD H. GRoss l *Si ATTORNEY hemd July 4, 1939 soLvEN'r nsrmNo mmaoosnnou on.

Bernard Y. McCarty and Howard H. Gross, Beacon, N. Y., assignors to The Texas Company,

New York, N. Y., a

corporation of Delaware Application November 5, 1936, Serial No. 109,234

3 Claims.

This invention relates to solvent rening hydrocarbon oil, and more particularly solvent refining of mineral lubricating oil.

The invention contemplates a process of sol- 5 vent refining in which the oil is subjected to a primary extraction with a selective solvent to form extract and railinate phases. The more paraiinic constituents of the extract phase, formed in the primary extraction, are removed l0 and separately subjected to re-extraction with a selective solvent. The process involves saltingout or separating these more paraiinic constituents of the primary extract phase by treating the primary extract phase with heavy extract phase material from which the solvent has been removed, all or in part, and fromfwhich the relatively parailinic constituents have been removed.

More specifically, the invention contemplates effecting primary extraction with a solvent, such p0 as urfural, to produce a railinate phase containing high viscosity index constituents, and an extract phase comprising low viscosity index constituents and constituents of intermediate as well as relatively high viscosity index dissolved in the 3s bulk of the solvent.

The extract phase is then treated so as to separate therefrom a fraction comprising constituents of the oil of intermediate and relatively high viscosity index, and which will be referred to as intermediate oil. This intermediate oil is separated from the extract phase by mixing with the extract phase a suitable proportion of extract material, accumulating in the subsequent steps of the process, from which the intermediate oil has been removed and from whichjthe solvent has also been removed, all or in part.

We have found that the addition of this heavy extract material, from which the solvent and intermediate oil has been removed, to the extract phase produced in the primary extraction exerts a salting-out effect such that the intermediate oil is separated from the extract phase to a very high degree. The separation of the intermediate oil so obtained is more efficient, and a higher yield is obtained than when the extract phase is subjected merely to cooling and settling.

The intermediate oil so obtained is then ex- I oil products from the initial charge stock than is realized where the intermediate oil is returned to the primary extraction zone and re-extractec in the presence of the fresh charge.

While furfural has been mentioned, it is contemplated that other solvent compounds, having selective action as between constituents of the oil of differing viscosity indices, may be employed. For example, other solvents may comprise aniline, benzaldehyde, nitrobenzene, etc. The selective solvent may be used alone, or in the presence of a suitable modifying solvent. `Among the modilying solvents which may be used are benzol or one of its homologs; light petroleum hydrocarbons such as propane, butane, natural gasoline or its constituents; and naphtha. Low-boiling aliphatic ethers may be used, such as ethyl and isopropyl ether.

In order to more fully describe the invention, reference will now be made to the accompanying drawing. f

As shown in the drawing, the oil to be treated is introduced to the lower portion of an extraction tower l, while the selective solvent is introduced to the upper portion of the ytower. 'Where the selective solvent is lighter than the oil undergoing treatment, it is, of course, contemplated that the points of entry of the solvent and oil will be reversed.

The solvent and oil ow countercurrently in direct contact with each other through the tower. Contact between the two bodies is facilitated by providing suitable contacting surfaces within the tower.

The raffinate phase comprising high` viscosity index oil of arounda 100' viscosity index accumulates in thetop of the tower and is removed therefrom as a primary raflinatephase. The solvent is removed from this phase by distillation, and the remaining oil subjected to such further treatment as may be desired.

The extract phase accumulating in the bottom of the tower is removed as a primary extract l phase and conducted through a mixing coil 2 to a settler 3. In the mixing coil, the extract phase is mixed with heavy extract material accumulating in a subsequent step of the process, as will be explained below. This heavy extract material is introduced to the mixer from a pipe l. It may be mixed with the extract phase in the proportion of from one `to five parts of extract material to twenty parts of primary extract phase.

The mixture is allowed to stand in the settler 3, either with or without cooling. Where cooling is desired, it may be accomplished by submerging The intermediate oil is removed and conducted k to the lower portion of a secondary extraction tower 5 wherein it is brought into countercurrent contact with fresh solvent introduced to the upper portion of the tower. The rafllnate phase accumulating in the top of the tower is removed therefrom as a secondary rainate phase.

By adjusting the conditions of temperature and solvent dosage, this secondary railinate oil, after removal of the solvent, may be such as to have practically the same viscosity index as the primary railinate where the primary ramnate ranges from 75 to 85 in viscosity index. Where the pri. mary raiilnate oil ranges from 85 to 100 in viscosity index, this secondary` railinate oil will be from about two to ten points below the primary raiilnate oil in viscosity index.

The extract phase accumulating in the lower portion of the secondary tbwer is removed therefrom as a secondary extract phase and is conducted to a stripper 6 wherein the solvent is removed by distillation, preferably in the presence of steam.

Referring again to the settler 3, the layer of extract material and solvent accumulating in the bottom thereof is withdrawn to a stripper l wherein the solvent is also removed by distillation, all or in part. The residue accumulating in the bottom of the stripper 1, and known as primary extract, is withdrawn, and the required proportion thereof returned through the pipe 4 to the mixer 2.

If desired, the material accumulating in the bottommoi the stripper 6, and referred to as a secondary extract, may be returned in part through the pipe l to the mixer 2. It is oontemplated that either primary extract or secondary extract, or a mixture of the two, may be returned to the mixer 2 for addition to the primary extract phase.

In some instances, it is contemplated that it may be advantageous merely to strip a suitable proportion of the solvent from the primary extract phase, and then subject the remaining mixture to settling in order to separate the intermediate oil therefrom. This maybe resorted to,

for example, where the ratio of solvent to oil in the primary extraction has been relatively large. In that case, the primary extract phase is conducted directly to a stili 8 wherein `the desired amount of solvent liquid is removed therefrom. The remaining extract phase material is then withdrawn from the still and conducted to the settler 3 wherein it may be subjected to settling, either with or without cooling. Where cooling is desired, it may be imparted by circulating a cooling medium through a coil 9 provided within the settler 3 as shown.

The removal of the solvent causes aconcentration of oil in the extract phase so that the relatively insoluble and more paraiinic constituents will more readily separate from the mixture upon settling.

The. residue from the still 8 may also be introduced to the mixer 2 and there mixed with heavy extract material prior to introduction to the settler I.

, proportions in both towers.

In carrying out theforegoing operation, where furiural is used as the selective solvent, the temperatures in the primary extraction towerl may range from 220 to 280 F. while the temperatures in the secondary extraction tower may be the same or range from around 190 to 250 F. It is advantageous to maintain a temperature differential through the tower between the points of solvent and oil introduction, the top of the tower being at the higher temperature.

The solvent may be introduced to the primary tower in the proportion of around two to eight parts oi' solvent to one part of oil, while in the secondary tower it may be used in the proportionof around one to four parts of solvent to one part of intermediate oil. It is contemplated, however, that, in some instances, depending upon the nature of the stock, it may be advantageous to use similar temperatures and similar solvent On the `other hand, it may be desirable to employ higher temperatures or higher solvent dosages, or both, in the secondary extraction tower.

We have carried out a number of tests showing the amount of intermediate oil separated by treating a primary extract phase with different amounts of heavy extract material. The extract phase in question was obtained by extracting (corresponding to the above described primary extraction) a distillate lubricating oil stock derived from lVIid-Continent crude, having a gravity of 23.4 and a Saybolt Universal viscosity at 210 F. of 102 seconds. 'Ihis stock was extracted with furfural in a countercurrent' tower with a temperature at the top of 264 F. and at the bottom of 20i F., using ilve parts of furfural to one part of oi The resulting primary extract phase comprised about 10% oil and 90% solvent by volume. A

' sample of this extract phase, with the solvent removed, had an A. P. I. gravity of 13.3 and a Saybolt Universal viscosity of 224.5 seconds at 210 F.

It was found that:

A. When 200 cc. of this extract phase, containing 10% oil and 90% furfural, was cooled from 200 F. to 130 F., the amount of intermediate oil separating was 10 cc.

B. 200 cc. of the original extract phase referred to in A was then mixed'with 100 cc. of extract phase from which the 10 cc. intermediate oil had been removed but which still contained the solvent. When this mixture was cooled from 200 F. to 130 F., the intermediate oil which separated amounted to 14 cc.

C. 200 cc. of the original extract phase referred to in A was mixed with 100 cc. of extract material from which, in addition to the removal of the intermediate oil, about 40% of the solvent had been stripped. When cooling this mixture from 200 F. to 130 F., the amount of intermediate oil which separated was 35 cc.

D. On the other hand, when 200 cc. of the original extract phase referred to in A was mixed with 10 cc. of extract material, from which both the intermediate oil and all of the solvent had been removed, there was a separation upon cooling, through the same temperature range, of only cc. of oil.

These examples show that by mixing the primary extract phase with extract phase from which the intermediate oil has been previously removed, and cooling the mixture from 200 F. down to 130 F., much more intermediate oil is separated than when the original primary extract man 3 phase is cooled in the absence of the heavy extract material. The data also show that the maximum yield of intermediate oil separated is obtained by employing as the salting-out agent extract phase material from which about half of the solvent has been stripped in addition to the removal of the intermediate oil.

Obviously, many modiilcations and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. In the refining of hydrocarbon oil by solvent extraction to separate the oil into fractions of different viscosity index, the method which comprises extracting the oil with ajselective solvent in a primary extraction zone, forming a primary ralnate phase containing oil of high viscosity index and a primary extract phase containing oil of intermediate and low viscosity index, separately withdrawing said phases from the primary extraction zone, incorporating in the withdrawn primary extract phase a precipitant'consisting of a separate portion of primary extract phase from which has been removed such oil as separates upon settling the primary extract phase at a temperature substantially below that at which the primary extract phase was formed and from which about half of the solvent has been removed, subjecting the withdrawn primary extract phase containing the incorporated precipitant to settling, thereby forming an oil phase comprising oil of intermediate viscosity index and a heavy extract phase comprising oll of low viscosity index, and separating said phases.

2. In the refining of hydrocarbon oil by solvent extraction to separate the oil into fractions of different viscosity index, the method which comprises extracting the oil with a selective solvent in a primary extraction zone, forming a primary ramnate phase containing oil of high viscosity index and a primary extract phase containingl oil of intermediate and low viscosity index, separately withdrawing said phases from the primary extraction zone, incorporating in the withdrawn primary extract phase a precipitant consisting of a separate portion of primary extract phase from which has been removed such oil as separates upon settling the primary extract phase at a temperature about '10 F. below the temperature at which the primary extract phase was formed and from which about half of the solvent has been removed, subjecting the withdrawn primary extract phase containing the incorporated precipitant'to settling, thereby forming an oil phase comprising oil oi' intermediate viscosity index and a heavy extract phase comprising oil of low viscosity index, and separating said phases.

3. In the rening of mineral lubricating oil by extraction with furfural, the method which comprises extracting the oil with furi'urai in a primary extraction zone at a temperature of around 200 F. and above, forming a primary railinate phase containing high viscosity index oil and a primary extract phase comprising low and intermediate viscosity index oil dissolved in the bulk of the solvent, separately withdrawing said primary phase, incorporating in the primary extract phase a precipitant consisting of a separate portion of primary extract phase from which has been removed substantially all of the oil that separates upon settling the primary extract phase at a temperature of about 130 F. and from which about half of the solvent has been removed, subjecting the withdrawn primary extract phase containing the incorporated precipitant to settling, thereby forming an oil phase comprising oil of intermediate viscosity index and a heavy extract phase comprising oil of low viscosity index, and separating said phases.

BERNARD Y. MCCARTY. HOWARD H. GROSS. 

